Method of making probe cards

ABSTRACT

A method and apparatus for inspecting integrated circuit probe cards in which the probe points of the probe card are scanned across a checkplate having a conductivity transition border. The impedances between the probe points and the checkplate as they cross the conductivity transition border are measured to determine when the probe points cross the border. The positions of the probe card when each of the probe points crosses the border are measured to determine the positions of the probe points relative to each other. In one embodiment, the checkplate is formed by a square conductive plate having three quadrants of insulated material and a single quadrant of conductive material mounted on its upper surface. These conductive strips connected to the conductive plate are positioned between the quadrants of insulative material to form the conductivity transition border. In other embodiments, multiple parallel strips or a single dot of conductive material are surrounded by insulative material.

This application is a division of U.S. patent application Ser. No.07/254,269, filed Oct. 5, 1988 now U.S. Pat. No. 4,918,379 issued Apr.17, 1990.

DESCRIPTION

1. Field of the Invention

This invention relates to the field of testing integrated circuitsduring manufacture, and more particularly, to a method and apparatus forinspecting probe cards that are used to make contact with integratedcircuits so that the integrated circuits can be tested while they arestill part of the wafer on which they were formed.

2. Background Art

In the semiconductor industry, there is a need to performance testindividual integrated circuits, or "chips," while they are still intheir parent wafer. In order to conduct performance tests on thesechips, electrical contact must be made with bonding pads formed on theintegrated circuit so that appropriate electrical stimulus can beapplied to the chips and their respective responses can be determined. Adevice known as a "probe card" is normally used to make contact with thebonding pads of integrated circuits to allow performance testing.

Probe cards consist of an array of resilient conductors or wiresterminating in an array of respective probe points. The wires formingthe array of probe points are mounted on a printed circuit board, andthe probe points are positioned so that they are precisely aligned withthe integrated circuit's bonding pads. A different probe card isgenerally used for each type of integrated circuit since the bonding padpatterns vary with each integrated circuit. During use, an integratedcircuit is positioned below the probe array, with the probe pointsaligned with respective bonding pads. The wafer and probe array are thenbrought together so that the probe points slightly deflect as they makecontact with their respective bonding pads. The electrical stimuli andresponses to the stimuli are conducted through the probe card wires tosuitable electronic testing devices. The probe card and integratedcircuit are then separated, and the probe points are aligned withanother integrated circuit on the wafer to repeat the test until all ofthe integrated circuits on the wafer have been tested.

In order to maximize production efficiency and minimize the possibilityof chip damage, it is desirable to inspect the probe cards to verifytheir required electrical characteristics and probe point alignmentaccuracy. The inspection should be done prior to the card's first useand at subsequent intervals to check for wear, damage, or otherdegradation.

Some of the necessary electrical and mechanical inspections can beperformed by currently available devices. For example, machines arecommerically avialable to measure the planarization of probe cards. Theterm "planarization" refers to the degree of alignment of the probepoints in the vertical direction so that they occupy a common horizontalplane. A lack of planarization causes some of the probe wires to bendexcessively in order to ensure that all of the probe points make contactwith the integrated circuit. This excessive bending of probe wires cancause the probe points to excessively scrape the metal bonding pads thusruining the chip and producing accelerated wear and oxide buildup on theprobe points. Conventional probe card planarization measuring devicesfunction by positioning a flat metal plate adjacent and parallel to theprobe point array and then bringing the plate and array together insmall increments. After each incremental movement, the electricalcontinuity between each probe point and the metal plate is measured. Theposition at which a point makes contact with the plate and initiatescontinuity determines its position along the Z axis relative to theother points. The plate and array are progressively brought togetheruntil all of the probe points have made contact with the plate, thusallowing the Z axis positions of all of the probe points to bedetermined.

An important electrical characteristic of probe cards is the contactresistance of their probe points. The contact resistance of the probepoints gradually increases with use as metal oxides and othercontamination adhere to the probe points. Contact resistance is thusmeasured to determine when the probe points must be cleaned. Contactresistance can be measured by connecting an ohm meter in series with theprobe wires as they make contact with the plate of a probe cardplanarization measuring device.

Another electrical parameter of probe cards which can be measured withan ohm meter is the "board leakage." The "board leakage" is caused bycontamination of the probe card and is inversely proportional to theresistance between the probe wires of the card when the wires areisolated from each other and from the planarization plate.

One very important parameter of a probe card that must be measured isthe alignment of the probe points along the X and Y axes relative to thebonding pads. The X and Y axes alignment of probe points are currentlymeasured optically by positioning the probe array over its correspondingintegrated circuit. The probe array is placed in contact with thebonding pads of the integrated circuit, and the probe wires aredeflected an appropriate amount. The positions of the probe pointsrelative to respective bonding pads are then examined visually through amicroscope.

This conventional approach to inspecting the probe point alignment alongthe X and Y axes exhibits a number of limitations. First, since theintegrated circuit itself is used to assess the probe point alignment,the probe point alignment cannot be inspected until a correspondingintegrated circuit or its artwork has been produced. Thus, it is notpossible to inspect the probe cards for an integrated circuit until theintegrated circuit is in production. Second, the conventional techniqueis inherently subjective and labor-intensive, with its attendant expenseand susceptibility for errors. Although the need exists forautomatically measuring probe point alignment along the X and Y axes, asuitable machine has not been developed.

As mentioned above, it is currently not possible to inspect probe pointalignment until a corresponding integrated circuit or its artwork hasbeen produced. It is also not possible to manufacture probe cards usingconventional techniques until corresponding integrated circuits ormetalization artwork have been produced. Probe cards are currentlymanufactured by mounting a wafer containing a large number of integratedcircuits and a sheet of Mylar on the same table. An operator aligns aviewing aperture with each of the bonding pads on an integrated circuitof the wafer, and punches a hole in the Mylar at a location that isspaced a fixed distance from the optical aperture. An array of holes isthus punched in the Mylar sheet at locations corresponding to thepositions of the bonding pads of the integrated circuit. Pointed probewires are then placed through each of the holes in the Mylar and aresecured to a printed circuit card by a suitable adhesive. After theadhesive has hardened, the Mylar sheet is removed, leaving the wires attheir proper locations. The wires are then sanded to make their pointsflat and the array planar. An integrated circuit is thus a criticalcomponent in the manufacture of the Mylar sheet used to position theprobe wires for the corresponding probe card, thereby making itimpossible to manufacture probe cards until corresponding integratedcircuits or its artwork have been produced.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide automatic inspectionof probe point alignment for integrated circuit probe cards.

It is another object of the invention to provide automatic inspection ofessentially all probe card electrical parameters with a singleinspection machine.

It is another object of the invention to allow inspection of probe pointalignment before corresponding integrated circuits or their artwork havebeen produced.

It is another object of the invention to provide an automatic inspectionsystem that, in addition to inspecting probe point alignment, can alsomeasure the transverse dimensions of the portion of the probe pointsthat make contact with the plate or chip.

It is another object of the invention to provide a means ofautomatically measuring the position and orientation of the probe arrayrelative to indexing features on the probe card so that this positionalinformation can be used during the setup of a probe machine.

It is another object of the invention to provide a means of measuringthe X-Y locations of the probe points when they are vertically deflectedinto the same positions they are in when being used in chip testing sothat any lateral point movement that occurs during the verticaldeflection is taken into account during the X-Y measurements.

It is another object of the invention to provide a means of facilitatingthe repairing, or bending, of the probes into proper alignment.

It is still another object of the invention to automatically generate areference file of probe point locations to assist in aligning the probecard with integrated circuits during testing of a wafer of integratedcircuits.

It is a further object of the invention to allow probe cards to bemanufactured before their corresponding integrated circuits or artworkhave been produced.

These and other objects of the invention are provided by a system forinspecting an integrated circuit probe card having a plurality of probewires terminating in respective probe points arranged in a probe pointarray. The system includes an X-Y table on which a checkplate ismounted. The checkplate has a planar measurement surface in which aconductivity transition border is formed so that the resistance betweenthe surface of the checkplate and a measurement terminal varies betweentwo values on opposite sides of the border. The probe card is mountedadjacent the checkplate, with its probe points contacting themeasurement surface. A control system drives the X-Y table to cause theprobe point array to scan across the measurement surface of thecheckplate from one side of the conductivity transition border to theother. An impedance measuring circuit measures the impedance betweeneach probe wire and the measurement terminal of the checkplate toidentify when each of the probe points reaches the border. Thehorizontal location of the checkplate relative to the probe card wheneach of the probe points crosses the conductivity transition border ismeasured to determine the locations of the probe points relative to eachother. In one embodiment, the checkplate includes a conductive base, aregion of conductive material mounted on the base, and a layer ofinsulative material mounted on the base and surrounding the conductivematerial. The measurement terminal is thus formed by the conductivebase, and the conductivity transition border is formed by the interfacebetween the conductive material and the insulative material. The regionof conductive material may be in the form of a dot having a maximumtransverse dimension that is smaller than the distance between adjacentprobe points of the probe card. Alternatively, the region of conductivematerial may have a linear periphery so that the conductivity transitionborder forms a straight line. A second linear conductivity borderextending in a direction that is perpendicular to the first linearconductivity border may also be mounted on the base. As a result, thepositions of the probe points along one axis of a Cartesian coordinatesystem can be determined by scanning the probe points across the firstlinear border. The positions of the probe points along the other axis ofthe Cartesian coordinate system can be determined by scanning the probepoints across the second linear border. In the event that there are twoconductivity transition borders parallel to each other, the controlsystem can determine the location of the probe points by averaging thepositions of the probe card when the probe points reach the firstconductivity border with the positions of the probe card when the probepoints leave the second conductivity border. The transverse dimension ofthe probe points can also then be determined by calculating thedifference between the positions of the probe card when the probe pointsreach the first conductivity border with the positions of the probe cardwhen the probe points leave the second conductivity border and deductingthe lateral dimension between the conductivity transition borders.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially exploded plan view of a semiconductor wafer havinga large number of integrated circuits formed thereon.

FIG. 2 is an isometric view of a conventional integrated circuit probecard used to test integrated circuits while they are still on a wafer.

FIG. 3 is an isometric view of a checkplate used to inspect for probepoint alignment in accordance with the present invention.

FIGS. 4a-4d are mechanical schematic illustrating the manner in whichprobe point alignment is measured using the checkplate of FIG. 3.

FIG. 5 is a mechanical and electrical schematic illustrating anembodiment of an inspection machine using the checkplate of FIG. 3.

FIG. 6 is an electrical schematic of an electrical circuit used in theembodiment of FIG. 5.

FIGS. 7A and 7B are flow charts of the software controlling theoperation of the embodiment of FIG. 5.

FIG. 8 is a top plan view of an alternative embodiment of a checkplatethat can be used in the inspection machine of FIG. 5.

FIG. 9 is a top plan view of another alternative embodiment of acheckplate that can be used in the inspection machine of FIG. 5.

FIG. 10 is a top plan view of another alternative embodiment of acheckplate that can be used in the inspection machine of FIG. 5.

BEST MODE FOR CARRYING OUT THE INVENTION

A typical semiconductor wafer 10, as illustrated in FIG. 1, includes athin, cylindrical plate 12 of semiconductor material, such as silicon. Alarge number of integrated circuits, generally indicated at 14, areformed on the surface of the wafer 10 by conventional semiconductorfabricating techniques. The integrated circuits 14 are typicallyarranged in rows and columns. After each of the integrated circuits isfunctionally tested, the wafer 10 is sliced along the rows and columnsto form a large number of semiconductor "chips," each of which containsan integrated circuit.

The integrated circuit 14 includes a large number of transistors,diodes, and other electronic devices, generally indicated at 16. Thecircuit formed by the components 16 is connected by conductors to aplurality of bonding pads 18, generally arranged in a line along thesides of the integrated circuit 14. The bonding pads 18 are typicallyformed from a metal, such as aluminum. The integrated circuit chip 14 isnormally mounted on a substrate, and the bonding pads 18 are connectedto conductor pins through thin wires bonded to the pins and the bondingpads 18. The integrated circuit is then hermetically sealed by a ceramicor metal enclosure.

The integrated circuits 14 are actually substantially smaller than theyare illustrated in FIG. 1. The extremely small size of each integratedcircuit 14 results in bonding pads 18 that are spaced very close to eachother. In order to perform functional tests on the integrated circuits14 when they are still a part of the wafer 10, it is necessary tosimultaneously make contact with all of the bonding pads 18 in a mannerthat does not interconnect adjacent bonding pads 18. Further, contactwith the bonding pads 18 must be made very quickly in order to test thelarge number of integrated circuits 14 in a reasonable period of time.Integrated circuit probes that are used to make contact with the bondingpads must, therefore, have probe points that are precisely positioned tocorrespond to the positions of the bonding pads 18.

A probe card used to make contact with the bonding pads 18 of integratedcircuits 14 is illustrated in FIG. 2. The probe card 20 includes aconventional printed circuit board 22 having a circular cutout 24.Printed circuit conductors, generally designated by reference numeral26, are formed on the board 22. The conductors 26 extend from one edge30 of the board 22 to a plurality of pads 32 arranged around thecircumference of the circular cutout 24. The printed circuit conductors26 adjacent the edge 30 of the board 22 are adapted for insertion into aconventional printed circuit board edge connector (not shown). Aplurality of probe wires 36 are bonded to respective mounting pads 32,such as by soldering. The wires 36 terminate in respective probe points38 that together form a probe point array 40.

In operation, conventional electronic testing instrument are connectedto the probe wires 36 through the conductors 26 and edge-mountedconnector. Stimulus signals and power are then applied to the integratedcircuit through the probe wires 36, and the responses to the stimulusare measured through the probe wires 36, conductors 26, and theedge-mounted connector. After the test has been completed, the probearray 40 is lifted from the bonding pads 18 of the integrated circuit 14and moved over to another integrated circuit 14. The probe points 38 arethen aligned with the mounting pads 18 of the integrated circuit and theprobe card 20 is moved against the integrated circuit 14 until the probewires 36 have been deflected by a predetermined value. Testing is thenconducted on that integrated circuit 14. The above described procedureis repeated until all of the integrated circuits 14 have been tested.

One embodiment of a checkplate that can be used to check the probe pointalignment of probe cards is illustrated in FIG. 3. The checkplate 50includes a plate 52 of rigid material, such as steel, which ispreferably conductive. The upper surface of the plate 52 is divided intofour quadrants, one of which is formed by a conductive surface 54 andthe others of which are formed by insulating surfaces 56, 58, 60separated from each other by conductive strips 62, 64. The conductivestrips 62, 64 preferably make contact with the plate 52. Thus, aconductive object on the conductive quadrant 54 is electricallyconnected to the plate 52. However, conductive objects on the insulatingsurfaces 56, 58, 60 are electrically isolated from the plate 52. Aconductor sliding along insulating surface 56 to insulating surface 58is thus connected to the plate 52 only when it crosses the conductiveline 62. Similarly, a conductor sliding along insulating surface 58 toinsulating surface 60 is connected to the plate 52 only when it crossesconductive line 64.

The manner in which the checkplate 50 is able to inspect the alignmentof a probe point array along all 3 (X, Y and Z) axes is best illustratedin FIG. 4. As illustrated in FIGS. 4A and 4B, the probe point array 40is initially positioned above the conductive surface 54, and the probepoint array 40 and conductive surface 54 are moved toward each otherwhile the resistance between each of the probe wires 36 (FIG. 2) and theconductive plate 52 is measured. The position of the probe card 20 alongan axis normal to the planar surface of the checkplate 50 is recordedwhen one of the probe points 38 first makes contact with the conductivesurface 54. The identity of the particular probe point 38 making contactwith the surface 54 is also, of course, recorded. In a similar manner,the probe point array 40 and the conductive surface 54 are incrementallybrought together, and the position of the probe card 22 along an axisnormal to the surface 54 is measured and recorded, as each of the probepoints 38 makes contact with the conductive surface 54. The resultingrecord indicates the planarization, or Z-axis positions, of the probepoint array 40. It will be understood, of course, that the Z-axispositions of the probe points can be measured either before or after theX-axis and Y-axis positions of the probe points are measured. Also, thecheckplate 50 can be used solely to measure either the Z-axis positionsof the probe points or the X-axis and Y-axis positions of the probepoints.

If all of the probe points 38 make contact with the conductive surface54 at substantially the same position of the probe card 22, then theplanarization is considered to be very satisfactory. If, however, thereis a substantial difference in the positions of the probe card 20 fromthe position at which the first probe point 38 makes contact with theplanar surface 54 and when the last of the probe points 38 makes contactwith the surface 54, then the degree of planarization may be consideredunsatisfactory.

Before or after the planarization test has been conducted, the probearray 40 is placed over the insulating surface 56 near the conductiveline 62, as illustrated in FIG. 4C. The probe point array 40 is thenscanned across line 62 in the X direction. This scanning is accomplishedby bringing the probe array 40 and the insulating surface 56 toward eachother to deflect the probe points 38 to the same degree that they wouldbe deflected if they were contacting the bonding pads 18 of anintegrated circuit 14. Thus, the positions of the probe points 38 on theinsulated surface 56 correspond to the positions that the probe points38 would occupy on an integrated circuit 14 during test. After the probepoints 38 have been deflected by a predetermined value, the resistancebetween each of the probe wires 36 (FIG. 2) and the conductive plate 52is measured to determine if any of the probe points are contacting theconductive line 62. The probe points are then lifted from the insulativesurface 56 and moved incrementally a small distance along the X-axis.The probe array 40 and the conductive surface 56 are once again broughttogether to deflect the probe points 38 by a predetermined value, andthe resistance between each probe wire 36 and the conductive plate 52 ismeasured. Whenever any of the probe points 38 contact the conductivestrip 62, the position of the probe card 20 is recorded. Also, when eachof the probe points 38 subsequently moves off the conductive strip 62onto the insulating surface 58, the position of the probe card 20 ismeasured and recorded.

After the probe array 40 has been moved along the X-axis so that all ofthe probe points 38 are contacting the insulating surface 58, two valuesof X will have been recorded for each probe point 38. The first value isthe position of the probe card 20 when the probe point 38 first madecontact with the conductive strip 62. The second value is the positionof the probe card 20 when the probe point 38 lost contact with theconductive strip 62. These two values are averaged to provide a singlevalue indicative of the relative position of the center of each probepoint 38 in the probe point array 40. Further, the difference betweenthe two values, less the width of the conductive strip, for each probepoint 38 is an indication of the transverse dimension of that portion ofthe probe point 38 making contact with the checkplate along the X-axis.

After a table of X values has been obtained for the probe point array40, the probe point array 40 is placed over the insulating surface 58near the conductive line 64, as illustrated in FIG. 4D. The probe pointarray 40 is then scanned over the conductive line 64 in the Y directionin the same manner that the array 40 was scanned over conductive line 62in the X direction, as explained above with reference to FIG. 4C. Theresult is a table of two Y values for each probe point 38. Thedifference between these two Y values, less the width of the conductivestrip, is indicative of the transverse dimension of the probe point 38along the Y-axis, while the average between these two values provides asingle Y value for the center of each probe point 38. After the probepoint array 40 has been scanned across the conductive line 64 in the Ydirection, a table indicative of the relative positions of each probepoint 38 in two dimensions has been obtained.

While the conductive lines 62, 64 of the check plate 50 illustrated inFIGS. 3 and 4 are orthogonal to each other, it will be understood thatthey may intersect each at an angle of other other than 90 degrees.However, using conductive lines 62, 64 that intersect each other at 90degrees is preferred since it simplifies the derivation of X and Yvalues for each probe point 38.

Although conductive strips 62, 64 are used to determine the location ofprobe points in the embodiment of FIGS. 3 and 4, it will be understoodthat other designs may be used. For example, eliminating the conductivestrips 62 and 64 and making the surface 58 conductive rather thaninsulating provides a conductivity transition border between surface 56and 58 and between surface 58 and 60. This conductive transition bordercan be used to determine the X and Y locations of the probe points in amanner similar to the one explained above with reference to FIG. 4.However, using only one conductivity transition border (rather than twoconductivity transition borders provided by conductive lines) does notallow the transverse dimensions of the probe points 38 to be determined,nor does it allow the centers of the probe points 38 to be determined byaveraging two end values. Instead, the X and Y values correspond to thelocations of the probe points 38 when they first make contact with theconductive surface 58. Other alternative embodiments of checkplates aredescribed below.

One embodiment of a probe card inspection system is illustrated in FIG.5. The inspection system 70 includes a conventional X, Y, Z table 72mounted on a rigid machine base 74. The checkplate 50 is mounted on theX, Y, Z table 72 and connected to measuring electronics 76 throughconductor 78. The probe card 20 is secured to probe card holders 80 thatare mounted on the upper end of respective supports 82 extendingupwardly from the machine base 74. The probe wires 36 extend downwardfrom the probe card 20 to terminate in the probe points 38. The probewires 36 are also connected to the measuring electronics 76 through theprinted circuit conductors 26 (FIG. 2) and a multi-conductor cable 86.As described in greater detail below, the measuring electronics measurethe resistance between the checkplate 50 and each of the probe wires 36.The measuring electronics 76 are connected to a conventional computer 90operated by software that is described in detail described below.Computer 90 is connected to conventional circuitry 92 driving the X, Y,Z table 72 through a multi-conductor cable 94.

In operation, the computer 90 applies data to the control circuitry 92to cause the table 72 to position the conductive surface 54 (FIG. 3) ofthe checkplate 50 beneath the probe point array 40. The table 72 thenmoves the checkplate 50 upwardly by small increments while the measuringelectronics 76 monitor the resistance between the checkplate 50 and eachprobe wire 36. As the probe point 38 of each probe wire 36 makes contactwith the checkplate 50, the measuring electronics 76 output identifyingdata to the computer 90. The computer 90 then records the Z axisposition command that the computer 90 output to the table control 92.After all of the probe points 38 have made contact with the checkplate50, the computer 90 has recorded a table of values indicative of theplanarization of the probe point array 40.

The table 72, controlled by the computer 90 through the table control92, then moves the checkplate 50 to the position illustrated in FIG. 4Cand scans the probe point array 40 across the conductive line 62 whilethe measuring electronics 76 measure the impedance between each probewire 36 and the checkplate 50. When each probe wire 36 makes contact andthen loses contact with the conductive line 62, the measuringelectronics 76 output data identifying the probe wire 36 to the computer90. The computer 90 then records these two values along with the Xposition command output by the computer 90 when the two X values wererecorded. The computer 90 can then determine the center position of theprobe point 38 and the transverse dimension of the probe point 38 alongthe X axis. The table 72, acting under control of the computer 90through the table control 92, then moves the probe array 40 to theposition illustrated in FIG. 4D and scans the probe array 40 across theconductive line 64 in Y direction. The computer 90 records two Y valuesfor each probe point and calculates the center position and transversedimension in the Y direction for each probe point 38, as described abovewith reference to the X axis measurements.

The measuring electronics 76 are illustrated in FIG. 6 along with thecheckplate 50, probe card 20, and computer 90. The measurementelectronics 76 basically consist of a conventional integrated circuitmultiplexer (MUX) 100 having each of its inputs connected to arespective probe wire 36. The output of the multiplexer is applied to abuffer 102 formed by an inverter 104 having its input biased high bybattery 106 through resistor 108. The checkplate 50 is connected toground through conductor 78. The multiplexer 100 is controlled by a byteof data received from the computer 90. The computer 90 sequentiallyconnects each of the probe wires 36 to the input of the inverter 104according to the value of the control byte output to the multiplexer 100by the computer 90. When the input of inverter 104 is initiallyconnected to the probe wires 36, a high logic level is applied to theprobe wire 36 through a resistor 108 since the probe points 38 have notyet contacted the conductive line 62 (FIGS. 3 and 4). As a result, theinverter 104 will apply a logic "0" to an I/O port of the computer 90.When each probe wire 36 contacts a conductive surface of the checkplate50, the probe wire 36 is grounded, thereby pulling the input to inverter104 low to logic "0." The inverter 104 then applies a logic "1" to theI/O port of the computer 90. The computer 90 causes the multiplexer 100to connect each of the probe wires to the input of the inverter 104 todetermine if each of the probe wires 36 is connected to a conductive ornonconductive surface of the checkplate 50. The probe wires 36 areassociated with the current output of the inverter 104 by the value ofthe control signal that the computer 90 applies to the multiplexer 100.For example, if the output of inverter 104 is at logic "1" when thecomputer 90 causes the multiplexer 100 to be connected to probe pointnumber 10, the computer 90 can determine that probe point number 10 isconnected to a conductive surface of the checkplate 50. The computer 90is thus able to determine when each of the probe wires 36 makes contactwith a conductive surface of the checkplate 50.

As mentioned above, the computer 90 can be any of several commerciallyavailable computer systems. Further, it may be easily programmed in anyof several conventional programming languages in accordance with theflow chart illustrated in FIG. 7. With reference to FIG. 7, the programis initiated at 120 and immediately positions the conductive surface 54of the checkplate 50 beneath the probe array 40. The checkplate 50 israised an incremental amount at 122 to bring the checkplate 50 and probepoints 38 closer together. The multiplexer 100 switches the first probewire 38 to the input of the inverter 104 at 124, and the output of theinverter 104 is checked at 126. If the output of the inverter 104 islow, indicating that the probe wire is not contacting the checkplate 50,the program returns to 124 to cause the multiplexer 100 to check thenext probe wire. If the output of the inverter 104 is found to be highat 126, the program branches to 128, where the identity of the probepoint 38 and the current Z axis value of the checkplate 50 are recorded.The program then determines at 130 whether the multiplexer 100 hasscanned all of the probe wires. If all of the probe wires have not beenscanned, the program returns to 124 to increment the multiplexer 100 sothat it scans the next probe wire. If all of the probe wires 36 havebeen scanned, the program checks at 132 to determine if all of the probewires 36 have been read, i.e., if all of the probe points 38 havecontacted the checkplate 50. If some of the probe points 38 have not yetcontacted the conductive surface 54 of the checkplate 50, the programreturns to 122 in order to increment the X, Y, Z table in the Zdirection and raise the checkplate 50 an incremental amount. When all ofthe probe points 38 have contacted the checkplate 50, the positions ofall probe points 38 relative to each other along the Z axis have beendetermined. The computer 90 can then calculate the planarization of theprobe card 20.

After the Z axis planarization measurements have been made, the programbranches from 132 to 140 to position the checkplate so that the probearray 40 is above the insulating surface 56 adjacent conductive line 62,as illustrated in FIG. 4C. The computer 90 actuates the X, Y, Z table 72at 142 to move it an incremental distance in the X direction and raisethe checkplate 50 to deflect the probe wires by a predetermined value.The computer 90 then causes the multiplexer 100 (FIG. 6) to scan thefirst probe wire 36 at 144. The continuity of that probe wire 36 is thenchecked at 146. During the initial portion of the X positionmeasurements, the probe points 38 will be contacting the insulatedsurface 56 of the checkplate 50. The continuity check at 146 will thusindicate an open probe point 38, and the program will therefore branchto 148 to determine if an "X-CLOSE" value has been assigned to theprobe. An "X-CLOSE" value is assigned to the probe point 38 when theprobe point 38 contacts the conductive line 62. Thus, each of the probepoints 38 will initially not have an "X-CLOSE" value assigned to it, andthe program will branch to 150. The program determines at 150 if themultiplexer 100 has scanned all of the probe wires 36. Thus, after eachprobe wire 36 has been scanned, the program will return from 150 to 144to scan the next probe wire 36 until the final probe wire has beenscanned.

When all of the probe wires 36 have been scanned, the program willbranch from 150 back to 142 to lower the checkplate 50, incrementallymove the checkplate 50 in the X direction and then raise the checkplate50 at 142. Continuity of each of these probe wires 36 is once againchecked at 146. When each of the probe points 38 contacts the conductiveline 62, the conductivity check at 146 indicates a closed condition,thereby causing the software to branch to 156. The program determines at156 if an "X-CLOSE" value has previously been assigned to the probe wire36 currently being scanned. If an "X-CLOSE" value has not previouslybeen assigned, an "X-CLOSE" value is assigned at 158. If an "X-CLOSE"value for the currently scanned probe wire 36 has previously beenassigned, the program skips to 160. The program will branch from 156directly to 160 as the probe point 38 moves across the conductive line62 after an "X-CLOSE" value has been assigned to the probe point 38 whenthe probe point 38 first contacts the conductive line 62. The programdetermines at 160 if the multiplexer 100 has connected all of the probewires 38 to the inverter 104. If the multiplexer 100 has not yet scannedall of the probe wires 36, the program branches to 144, where themultiplexer 100 is incremented to the next probe wire 36, and thecontinuity of that probe wire 36 is checked at 146. After all of theprobe wires 36 have been scanned, the program branches from 160 to 142to lower the checkplate 50, incrementally move the checkplate in the Xdirection, and then raise the checkplate to deflect the probe wires 36by a predetermined value.

After the probe points 38 move from the insulating surface 56 to theconductive surface 62, they will eventually contact the insulatingsurface 58 as the probe array 40 moves across the conductive line 62 inthe X direction. Thus, after a closed continuity is detected at 156 foreach probe wire 36, an open continuity will subsequently be detectedwhen the probe point 38 contacts the insulating surface 58. At thistime, the software will branch to 148 to determine if an "X-CLOSE" hasbeen previously been assigned. In order for the probe point 38 to reachthe insulating surface 58, it must have made contact with the conductiveline 62 so that an "X-CLOSE" value will have been assigned. Accordingly,the program will branch to 170 to determine if an "X-OPEN" value haspreviously been assigned. When the probe point first makes contact withthe insulating surface 58, an "X-OPEN" value will not have beenassigned. The program will thus branch to 172 to determine if an X valuehas been stored in a temporary register. Once again, when the probepoint first contacts the insulating surface 58, an X value will not havebeen stored. As a result, the current position of the checkplate 50 isstored at 174, and a check is made at 176 to determine how manyconsecutive "opens" have been detected at 146. When the probe pointfirst contacts the insulating surface 58, there will be only a singleprobe location in which an "open" has been detected. Thus, the programwill initially branch to 178 to determine if all of the probe wires 36have been scanned. If all of the probe wires 36 have not been scanned,the program will return to 144 to cause the multiplexer 100 to check thenext probe wire 36 until all of the probe wires 36 have been checked, atwhich point the program will branch to 180. The program determines at180 whether "X-CLOSE" and "X-OPEN" values have been assigned to all ofthe probe wires 36. As the probe points 38 initially contact theinsulating surface 58, "X-OPEN" values will not have been assigned tothe probe wires 36. Thus, the program will branch to 142 to lower thecheckplate 50, move it an incremental distance, and then once againraise the checkplate 50 against the probe array 40. For a probe point 38contacting the insulating surface 58, the program will branch through144, 146, 148, 170 and 172 to 176. After the probe point 38 has madecontact with the insulating surface 58 "N" number of times, the programwill branch from 176 to 184 to assign the X value temporarily stored at174 as the "X-OPEN" value. Thus, when the probe point 38 initiallycontacts the insulating surface 58, the position of the checkplate 50 atthat point is temporarily stored. If the continuity of that probe point38 continues to be open for "N" measurements, the position of thecheckplate 50 when the probe point 38 initially contacted the insulatingsurface 58 is recorded as the "X-OPEN" value for that probe. The purposeof validating the X value as a true "open" is to prevent momentary lossof contact resulting from dirt, etc., on the checkplate 50 fromregistering as an "X-OPEN" value when the probe point is stillcontacting the conductive line 62.

After the program determines at 180 that all of the probes have beenassigned an "X-CLOSE" and an "X-OPEN" value, the program calculates theposition of each probe point along the X axis X₀ and the transversedimension of the probe point along the X axis X_(D) at 190. The probepoint position X₀ is calculated as one-half the sum of the "X-CLOSE" and"X-OPEN" value for that probe point 38, i.e., the average between theposition of the probe point 38 when it initially contacts the conductiveline 62 and its position when it initially contacts the insulatingsurface 58. The transverse dimension X_(D) of the probe point 38 iscalculated as the difference between "X-CLOSE" and "X-OPEN", less thewidth of the conductive strip, for that probe point 38. After all of theX values are calculated at 190, the program branches to 192 to positionthe checkplate so that the probe array 40 is over the insulating surface58 near the conductive line 64, as illustrated in FIG. 4D. Theabove-described procedure for scanning across the conductive line 62 toobtain X values is then repeated at 194 to scan the probe array 40across conductive line 64 to obtain Y values.

An alternative embodiment of a checkplate 200 is illustrated in FIG. 8.As in the checkplate 50, the alternative checkplate 200 is in the formof a single conductive square 202. However, instead of utilizing threeinsulating squares 56, 58, 60 separated from each other by conductivelines 62, 64, the alternative checkplate 200 utilizes a singleinsulating square 204 and two squares 206, 208 of alternating conductiveand insulating lines or strips. The strips in the square 206 extend inthe Y direction and are used for measuring the X positions andtransverse X dimensions of the probe array 40. The strips in the square208 extend along the X axis and are used to measure the Y positions andtransverse Y dimensions of the probe array 40. The primary advantage ofusing the check plate 200 illustrated in FIG. 8 is that is necessary tomove the checkplate 200 for an X and Y distance of approximately thewidth of one conductive strip and one insulating strip in order tomeasure all of the probe point positions. The conductive strips arepreferably wired separately so that it is possible to uniquely identifythe conductive strip and, therefore, the unique X position, that eachprobe point 38 is contacting.

Another alternative embodiment of a checkplate 220 is illustrated inFIG. 9. This checkplate 220 is similar to the checkplate 50 shown inFIG. 3, except that it utilizes conductive strips 222 for X axismeasurements that are divided into two electrically isolated strips222a, 222b. Similarly, strips 224a, 224b are electrically isolated fromeach other and used to make the Y axis measurements. As in thecheckplate 50, the alternative checkplate 220 utilizes a singleconductive square 226 and three insulative squares 228, 230, 232 whichare separated from each other by the conductive strips 222, 224.Utilizing conductive strips divided in two and electrically isolatedfrom each other allows measurements to be made on probe cards that havetheir probe wires 36 positioned on opposite sides of the probe array 40wired together. In this embodiment, the probe points 38 on one side ofthe array 40 have their X values determined by strip 222a and their Yvalues determined by strip 224a. The probe points 38 on the oppositeside of the array 40 have their X values measured by strip 222b andtheir Y values measured by strip 224b.

Still another embodiment of the checkplate 240 is illustrated in FIG.10. The checkplate 40 utilizes any of the combinations of conductor andinsulator described above, and has the addition of a small dot 250 ofconductive material formed thereon that is electrically isolated fromthe other conductors and is wired out to a separate terminal. The probearray 40 may be scanned across the dot 250 so that each of the probepoints 38 sequentially contacts the dot 250. The dot 250 should be smallenough that two probe points 38 cannot contact the dot 250 at the sametime. The checkplate 240 of FIG. 10 allows the alignment of probe cards20 to be checked in which some of the probe wires 36 are wired to eachother. The alignments of probe points 38 are checked by scanning theprobes across the dot 250 in a manner analogous to scanning probe pointswith the conductive strips 62 and 64.

The dot 250 may also be used as an aid in probe card 20 rework. Thiscould be done by first measuring the alignment of all the probe points38 in the manner described above. Next, a probe point 38 that requiredrework, or bending, to bring it into alignment relative to the otherprobe points 38, would be positioned over the dot 250 in such a way thatthe dot 250 is positioned where the probe point 38 would be if it wereaccurately aligned. An operator, looking through a microscope, would seethe displacement of probe point 38 from the dot 250 and would use atweezers to bend the probe point 38 into position over the center of thedot 250. The dot 250 could then be further used to check the position ofthe reworked probe point 38 to measure the success of the reworkoperation and again positioned for further rework if required.

An alternative embodiment of the checkplate would be to replace theinsulating squares with conducting squares and to replace the conductingstrips with insulating strips. This alternative checkplate would be usedin the same manner as the one described above but has the disadvantagethat it cannot determine the x and y locations of probe points that arewired together on the probe card.

The checkplates 50, 200, 220, 240 can be manufactured utilizing a numberof known manufacturing techniques. One manufacturing technique is to cuta thin sheet (e.g., 0.01 inch) of a suitable material, such as tungstencarbide, into strips about 0.1 inch wide. The upper surface of arelatively thick plate of steel is then divided into four quadrants bymachining grooves into its upper surface, the grooves having a width ofabout 0.05 inch. The strips cut from the plate are then turned on theiredge and inserted into the grooves in the plate and secured by fillingthe grooves with a suitable conductive epoxy. Three squares formed froma sheet of insulating material are then forced against the strips andsecured to three quadrants of the plate with a suitable adhesive.Finally, a square formed from a conductive sheet is secured to theremaining quadrant of the plate, with its edges contacting the adjacentstrips. The upper surface of the checkplate should be very hard andsmooth so that it is not worn down by the probe points 38 nor does itcause any significant wear of the probe points 38. Thus, after thecheckplate is fabricated as described above, it is preferably polishedto a fine surface finish.

Checkplates can also be manufactured by other processes, such as byusing photolithographic techniques to deposit or otherwise create a thinlayer of an insulator on the surface of a conductor or a thin layer ofconductor on an insulator. The boundary shapes of the deposits definingconductive transition borders would be defined by a photolithographicmask. Suitable chemical etching techniques can also be used.

It should be noted that since the above-described checkplates can beused to determine the location of probe points 38, they can also be usedto manufacture probe cards 20. Probe cards 20 can be manufactured byclamping each probe wire 36 in sequence in a holder. The checkplatewould be positioned, by the X, Y, Z table, at the probe point, in aprescribed sequence, to determine the exact location of the pointrelative to the holder features. This information would then be used toposition the probe card in the proper position relative to the point andthe probe would then be attached to the circuit board 22. The next probewire 36 is then held by the holder and its probe point 38 found andplaced at the proper location on the circuit board and attached. Theabove process is repeated until all of the probe wires have beenattached to the printed circuit board 22.

The data specifying the locations of the probe points 38 which areobtained using the checkplates can also be used to align the probe card20 with the integrated circuits on a wafer during testing. After theprobe point position measurements have been made with the systemdescribed in FIGS. 5-7, the location of each probe point 38 with respectto indexing features on the probe card is known. A "reference file" ofdata indicative of where each bonding pad on the chip will be located isalso obtained for integrated circuits prior to manufacture. Thus, eachintegrated circuit type has its own reference file. The centroid of theintegrated circuit can be obtained by averaging the positions of thebonding pads for the integrated circuit. Similarly, the centroid of theprobe point array 40 can be obtained by averaging the positions of theprobe points 38. The centroid of the probe array 40 can then be alignedwith the centroid of the reference file and a comparison made betweenthe locations of the bonding pads 18, as designated by the referencefile, with the measured positions of the probe points. A comparisonbetween the location of the bonding pads 18 and respective probe points38 allows an angle error to be calculated for each probe point/bondingpad pair. After all of the angle errors have been calculated for thereference point/bonding pad pairs, an average angle can be calculated.When the probe card 20 is used to test integrated circuits on the wafer,the probe card 20 can then be rotated by the average angle error toprovide the optimum fit between the probe point array 40 and the bondingpads 18. In a similar manner, the wafer can be offset by the X and Yerrors, relative to the indexing features, to provide the optimum X andY fit of the array to the bonding pads.

It is thus seen that the inventive method and apparatus for inspectingintegrated circuit probe cards allows all important electrical andmechanical parameters of probe cards to be inspected prior to placing acorresponding integrated circuit into production. Furthermore, it may beused to manufacture probe cards and optimizes the use of the probe cardsin testing integrated circuits.

We claim:
 1. A method of manufacturing probe cards for use in testingintegrated circuits, said probe card including a plurality of probewires terminating in respective probe points arranged in a probe pointarray, said method comprising:(a) providing a checkplate having a planarmeasurement surface with a conductivity transition border formed thereonin which the resistance between the surface of said checkplate and ameasurement terminal varies between two values on opposite sides of saidborder, said checkplate having a known position with respect to saidholder; (b) sequentially clamping each of said probe wires in a holder;(c) scanning said probe point across said border so that said probepoint contacts said measurement surface from one side of saidconductivity transition border to the other during said scan; (d)monitoring the impedance between said probe point and said measurementterminal during said scan in order to detect a change in impedancebetween said probe point and said measurement terminal when said probepoint reaches said conductivity transition border; (e) determining theposition of said probe card relative to said checkplate when a change inimpedance occurs for said probe point checkplate when a change inimpedance occurs for said probe point as said probe point reaches saidconductivity transition border, thereby determining the position of saidprobe point relative to said probe card; (f) attaching said probe wireto said probe card; and (g) repeating steps (b)-(f) until all of saidprobe wires have been attached to said probe card.